fix(dc-tool-b): 修复滚动条问题 - 适配MainLayout固定高度

- tool-b/index.tsx: min-h-screen  h-full overflow-y-auto
- 所有Step组件添加 h-full overflow-y-auto
- 修复：MainLayout改为固定高度后，工具B底部按钮可见性问题
- 效果：页面无滚动条，内容可内部滚动

frontend-v2/src/modules/dc/pages/tool-b/index.tsx

@@ -73,7 +73,7 @@ const ToolBModule: React.FC = () => {
   };
 
   return (
-    <div className="min-h-screen bg-slate-50 font-sans text-slate-800 p-6">
+    <div className="h-full bg-slate-50 font-sans text-slate-800 p-6 overflow-y-auto">
       <div className="max-w-7xl mx-auto bg-white rounded-2xl shadow-sm border border-slate-200 min-h-[800px] flex flex-col overflow-hidden">
         
         {/* Header */}
@@ -123,8 +123,8 @@ const ToolBModule: React.FC = () => {
           <StepIndicator currentStep={currentStep} />
         </div>
 
-        {/* Main Content */}
-        <div className="flex-1 px-8 pb-8 relative overflow-hidden flex flex-col">
+        {/* Main Content - ⭐ 修复：添加overflow-y-auto允许内部滚动 */}
+        <div className="flex-1 px-8 pb-8 relative overflow-y-auto flex flex-col">
           {currentStep === 'upload' && (
             <Step1Upload
               state={state}